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RE: st: data precision and problems therein


From   "Seed, Paul" <paul.seed@kcl.ac.uk>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   RE: st: data precision and problems therein
Date   Fri, 9 Nov 2012 14:12:42 +0000

Ngoc Minh PHAM points to a problem with non-integer cut-points.
He can solve it with the -float()- function:

Rather than 
	gen gly_haem_gt_6_1 = gly_haem > 6.1 

He can use 
	gen gly_haem_gt_6_1 = gly_haem > float(6.1)	

Or (allowing for missing values ) 
	gen gly_haem_gt_6_1 = gly_haem > float(6.1) if gly_haem <.

Or (perhaps easier to remember): 
	gen gly_haem_gt_6_1 = float(gly_haem) > float(6.1) if gly_haem <.

This is because his variable is stored as a float (7 decimal places more-or-less), 
but 6.1 is evaluated exactly (or at least to double accuracy).
Converting a float to exact is impossible (inventing extra decimal places); 
but going the other way is easy (just rounding). And float(float(x)) is the same as 
float(x), so extra float functions are not a problem.

If Ngoc prefers to cut the other way...
	gen gly_haem_ge_6_1 = float(gly_haem) >= float(6.1) if gly_haem <. 


Paul T Seed, Senior Lecturer in Medical Statistics, 
Division of Women's Health, King's College London
Women's Health Academic Centre, King's Health Partners 
(+44) (0) 20 7188 3642.

> Date: Fri, 9 Nov 2012 15:28:08 +0900
> From: Pham Ngoc Minh <minh.pn@tnu.edu.vn>
> Subject: st: data precision and problems therein
> 
> Dear statalist,
> 
> I have a problem with data precision as follows:
> 
> for example: glycated hemoglobin is 6.1 (%) visible in data editor,
> but it turns out 6.0999999 when clicked on, so are other numbers (5.6
> becomes 5.5999999), etc. This affects results of creating dummy
> variables with pre-defined cut-points of values. How about the
> solution?
> 
> Thank you for your advice
> 
> Ngoc Minh PHAM
> National Center for Global Health and Medicine, Japan.
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